The invention relates to a piston pump as generically defined by the preamble to the main claim, which is provided in particular for a hydraulic vehicle brake system.
One such piston pump is known from German Patent Disclosure DE 197 32 791 A1. The known piston pump has a pump bore, which is mounted in a hydraulic block that forms a pump housing. A piston is guided axially displaceably in the pump bore. In the known piston pump, a bush is inserted into the pump bore, and the piston is axially displaceably guided in the bush. It is equally possible to guide the piston axially displaceably in the pump bore in the pump housing directly, leaving out the bush. By mean of an eccentric element, which is disposed on one face end of the piston and is drivable to rotate, the piston can be driven to execute a reciprocating stroke motion in the axial direction in the pump bore, and this motion in a manner known per se brings about the pumping of fluid.
As disclosed in German Patent Disclosure DE 42 26 646 A1, for example, such piston pumps are typically followed hydraulically by a damper chamber and a throttle, both of which are disposed in the hydraulic block that forms the pump housing, outside the pump bore and separately from the piston pump.
A throttle which is disposed in the pump outlet is integrated with the piston pump of the invention as defined by the characteristics of claim 1. The throttle preferably hydraulically follows an outlet valve of the piston pump; that is, it is disposed downstream of the outlet valve of the piston pump. By way of example, the throttle, in the form of a baffle, nozzle or other cross-sectional constriction, can be disposed in the pump bore or in an outlet conduit in the pump housing. The throttle serves to damp pressure pulsations of the fluid pumped with the piston pump, which are caused by the piston pump because of its pulsating mode of pumping. Integrating the throttle with the piston pump has the advantage of dispensing with a separate throttle that requires accommodation externally, for instance in a hydraulic block. Another advantage is that a damper chamber downstream of the piston pump, which in known hydraulic vehicle brake systems is considered necessary, can be dispensed with.
Advantageous features and refinements of the invention defined by the main claim are the subject of the dependent claims.
In a preferred feature defined by claim 2, the piston pump of the invention has a bush, which is inserted into the pump bore in the pump housing, and in which the piston is guided axially displaceably. In this feature of the invention, the piston pump furthermore has a closure part, which closes the pump bore in pressure-tight fashion on one face end of the bush. An outlet conduit of the piston pump is formed by a groove, which is made in the closure part and/or in the bush and which either has or forms a narrowed point in order to form the throttle. This feature of the invention has the advantage of not requiring a separate component for the throttle; it enables favorable production of the throttle, and it has the advantage that the throttle occupies no additional space; that is, the throttle is integrated in a space-saving way with the piston pump.
The outlet conduit can be embodied for instance as a radial groove in an end edge of a tubular bush. In FIG. 3, the bush has a bush bottom on a face end toward the closure part. The outlet conduit is formed by a groove which is made in an end face of the bush bottom contacting the closure part and/or in a face of the closure part contacting the bush bottom, and which is covered by the closure part or the bush bottom, respectively. The groove has a narrowed point which forms the throttle.
A relief conduit according to claim 4 has the advantage that in the event of partial or complete clogging of the throttle, the closure part is pressure-relieved. If the throttle is clogged, then fluid pumped with the piston pump and emerging from an outlet hole, surrounded by the relief conduit, in the bush bottom flows into the relief conduit, as long as it passes between the faces contacting one another of the bush bottom and of the closure part, and from the relief conduit it flows past the throttle into the pump outlet downstream of the throttle. The effect of the relief conduit surrounding the outlet hole in the bush bottom is that fluid under pressure acts upon the closure part solely on the face enclosed by the relief conduit; that is, if the throttle is clogged, the stress on the closure part is limited to the fraction of the surface area, contacting the bush bottom, of the closure part that is enclosed by the relief conduit. As a result, clogging of the throttle is prevented from leading to leakage of the closure part in the pump bore or to forcing the closure part out of the pump bore in response to a high pressure on the outlet side of the piston pump resulting from the clogged throttle. This prevents self-destruction of the piston pump.
Producing the bush or the closure part as a formed part (claims 6, 7) has the advantage not only that these parts can be produced economically and quickly but also that the groove, forming the outlet conduit, in the bush bottom and/or in the face of the closure part contacting the bush bottom can be made in a single operation together with the production of the bush or the closure part as applicable. As a result, producing the throttle entails no additional effort or cost.
The piston pump of the invention is intended in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS (anti-lock brake system), TCS (traction control system), VDC (vehicle dynamics control) and EHB (electrohydraulic brake system) are used for such brake systems. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to pump brake fluid out of a supply container into a wheel brake cylinder or a plurality of wheel brake cylinders (TCS or VDC or EHB). In a brake system with wheel slip control (ABS or TCS) and/or a brake system serving as a steering aid (VDC) and/or an electrohydraulic brake system (EHB), the pump is needed. With wheel slip control (ABS or TCS), locking of the wheels of the vehicle during a braking event involving strong pressure on the brake pedal (ABS) and/or spinning of the driven wheels of the vehicle in the event of strong pressure on the gas pedal (TCS) can for instance be prevented. In a brake system serving as a steering aid (VDC), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the track desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB), in which the pump pumps the brake fluid into the wheel brake cylinder or cylinders if an electric brake pedal sensor detects an actuation of the brake pedal, or in which the pump is used to fill a reservoir of the brake system.